SPATIAL-RESOLUTION IN DIGITAL MAMMOGRAPHY

RATIONALE AND OBJECTIVES. Digital acquisition systems currently availa ble limit spatial resolution in digital mammography to roughly 0.1 mm/ pixel. The objective of this study is to determine if high-quality mam mography is possible at this resolution. METHODS. The influence of spa tial resolution on diagnostic quality was investigated by comparing ob server performance on film to that on digitized film. A 0.1-mm samplin g distance was used for digitization. Detection of mammographic detail s was studied by measuring threshold contrast as a function of detail size for small circular objects in the range of 0.12 to 2.5 mm. Charac terization of microcalcifications was investigated in a receiver opera ting characteristic (ROC) study, in which 10 radiologists read 72 mamm ographic details with microcalcifications, both digitally and on film. RESULTS. Digitization improved the detectability of the larger, low c ontrast objects, whereas for small objects the detectability did not c hange. The authors found that even under the most optimal circumstance s, isolated spherical calcifications with diameters smaller than 0.13 mm are not detectable with film-screen mammography, despite its resolu tion limit of 15 line patterns per mm (lp/mm). The ability to characte rize microcalcification clusters did not change significantly with dig itization. However, the results suggest that differentiation of benign from malignant cases decreases slightly, and that characterization of different types of malignancies somewhat improves by digitization. Me an differences between the two modalities were considerably smaller th an the interobserver variability. CONCLUSION. A relatively low spatial resolution of 0.1 mm/pixel does not prohibit high-quality diagnostic performance in digital mammography.